In the manufacture of tobacco products it is common practice to apply to the tobacco certain additives such as casing materials and top flavorings. Casing is usually applied to leaf strips or threshed leaf prior to cutting and generally includes humectants such as glycerol, diethylene glycol and propylene glycol along with flavoring materials such as sugar, cocoa and licorice. Top flavorings are generally applied to cut tobacco as a dilute solution in a volatile solvent such as ethanol. In either case it is important that these additives be applied to the tobacco as uniformly as possible at the desired use levels. Considerable attention has, therefore, been given to methods and apparatus for applying these additives to tobacco.
Apparatus that is used in the art for applying additives to tobacco includes a rotary drum provided with one or more spray nozzles through which the additives are applied to the tobacco as it tumbles on the inside surface of the rotating drum. Such apparatus is described, for example, in U.S. Pat. Nos. 3,419,015 and 4,054,145. A pneumatic system for applying a menthol solution to tobacco is disclosed in U.S. Pat. Nos. 3,548,838 and 3,678,939. An improved pneumatic system which avoids the use of solvents for applying menthol to tobacco is the subject of U.S. Pat. No. 3,800,806. Apparatus disclosed in U.S. Pat. No. 3,742,961 is directed primarily to stream treatment of tobacco but teaches incidentally the application of flavorants and other additives to the tobacco in conjunction with the steaming operation.
Although the inventions referred to in the foregoing patents are effective to a degree, certain disadvantages associated with one or more of these prior art devices are the high initial cost of equipment, high operational and maintenance costs, non-uniform or insufficient application of additives to the tobacco being treated, potential explosion hazards associated with volatile solvents used as a carrier for the additives and difficulty in confining volatile additives and-or solvents within the tobacco treating system.